/*
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
 */
package com.opensource.dbhelp.dbutils.handlers;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

import com.opensource.dbhelp.dbutils.ResultSetHandler;

/**
 * <p>
 * <code>ResultSetHandler</code> implementation that returns a Map. <code>ResultSet</code> rows are converted into objects (Vs) which are then stored in a Map under the given keys (Ks).
 * </p>
 *
 * @param <K>
 *            the type of keys maintained by the returned map
 * @param <V>
 *            the type of mapped values
 * @see com.opensource.dbhelp.dbutils.ResultSetHandler
 * @since DbUtils 1.3
 */
public abstract class AbstractKeyedHandler<K, V> implements ResultSetHandler<Map<K, V>> {

	/**
	 * Convert each row's columns into a Map and store then in a <code>Map</code> under <code>ResultSet.getObject(key)</code> key.
	 * 
	 * @param rs
	 *            <code>ResultSet</code> to process.
	 * @return A <code>Map</code>, never <code>null</code>.
	 * @throws java.sql.SQLException
	 *             if a database access error occurs
	 * @see com.opensource.dbhelp.dbutils.ResultSetHandler#handle(java.sql.ResultSet)
	 */
	@Override
	public Map<K, V> handle(ResultSet rs) throws SQLException {
		Map<K, V> result = createMap();
		while (rs.next()) {
			result.put(createKey(rs), createRow(rs));
		}
		return result;
	}

	/**
	 * This factory method is called by <code>handle()</code> to create the Map to store records in. This implementation returns a <code>HashMap</code> instance.
	 *
	 * @return Map to store records in
	 */
	protected Map<K, V> createMap() {
		return new HashMap<K, V>();
	}

	/**
	 * This factory method is called by <code>handle()</code> to retrieve the key value from the current <code>ResultSet</code> row.
	 * 
	 * @param rs
	 *            ResultSet to create a key from
	 * @return K from the configured key column name/index
	 * @throws java.sql.SQLException
	 *             if a database access error occurs
	 */
	protected abstract K createKey(ResultSet rs) throws SQLException;

	/**
	 * This factory method is called by <code>handle()</code> to store the current <code>ResultSet</code> row in some object.
	 * 
	 * @param rs
	 *            ResultSet to create a row from
	 * @return V object created from the current row
	 * @throws java.sql.SQLException
	 *             if a database access error occurs
	 */
	protected abstract V createRow(ResultSet rs) throws SQLException;

}